Gas Diffusion Layer for Fuel Cell, Method of Manufacturing the Same, and Unit Cell for Fuel Cell Including the Same

ABSTRACT

A gas diffusion layer for a fuel cell constituting a unit cell of the fuel cell includes a base layer including short carbon fibers and having a reinforcing portion formed in a predetermined area thereof in a thickness direction with continuous carbon fibers oriented in the reinforcing portion. One method of manufacturing the gas diffusion layer includes preparing a mixed dispersion in which short carbon fibers are mixed, orienting continuous carbon fibers on a conveyor belt, forming a paper having a reinforcing portion in which the continuous carbon fibers are oriented by supplying the prepared mixed dispersion to the conveyor belt on which the continuous carbon fibers are oriented, and forming a base layer by impregnating the paper with a hydrophobic agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2020-0181244, filed on Dec. 22, 2020, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a gas diffusion layer for a fuel cell,a method of manufacturing the same, and a unit cell for a fuel cellincluding the same.

BACKGROUND

A fuel cell, which is a kind of power generation deviceelectrochemically reacting chemical energy of fuel in a stack to convertthe chemical energy into electrical energy, can be used for industrialand household purposes, and used to not only supply power for driving avehicle but also supply power to a small electronic product such as aportable device. Recently, the applicable fields of the fuel cell haveincreasingly expanded because the fuel cell is a highly efficient cleanenergy source.

FIG. 1 is a view showing a typical unit cell for a fuel cell.

As can be seen from FIG. 1, a membrane-electrode assembly (MEA) 10 islocated on the innermost area of the typical unit cell for a fuel cell.The membrane-electrode assembly 10 includes a polymer electrolytemembrane ii capable of moving hydrogen cations (protons), and catalystlayers coated on both surfaces of the electrolyte membrane for hydrogenand oxygen to react, that is, an anode electrode layer (anode) 12 and acathode electrode layer (cathode) 13.

In addition, gas diffusion layers (GDLs) 20 are stacked on outer sidesof the membrane-electrode assembly 10, that is, on respective outersides of the anode electrode layer 12 and the cathode electrode layer13, and separators 30, each having a flow field formed to supply fueland discharge water generated by the reaction, are located on respectiveouter sides of the gas diffusion layers 20.

The separator 30 is a flow field type separator. The flow field typeseparator is bent so that lands 31 and channels 32 are alternatelyformed, the lands 31 are supported by the gas diffusion layer 20, andreaction gas flows through the channels 32. In this case, the lands 31and the channels 32 are formed to be aligned in one direction along areaction gas flow direction.

Meanwhile, the gas diffusion layer 20 is formed by forming a microporous layer (MPL) 22 on a base layer 21 made of carbon fibers.

In this case, the base layer 21 is generally formed by impregnating acarbon fiber paper with a hydrophobic agent such aspolytetrafluoroethylene (PTFE). As an example of the carbon fiber paper,carbon paper, carbon cloth, or the like may be used.

In addition, the micro porous layer 22 may be manufactured by mixing ahydrophobic agent such as PTFE with carbon powder such as carbon black,acetylene black carbon, or black pearls carbon, and then coated on onesurface or both surfaces of the base layer 21 according to the purposeof use.

Meanwhile, the carbon fiber base of the base layer 21 is formed in apaper type by forming a paper from short carbon fibers dispersed in anaqueous solution on a conveyor belt. As a result, the short carbonfibers are randomly oriented in a two-dimensional (2D) direction.Subsequently, a binder is heat-treated, the carbon fiber paper isimpregnated with a hydrophobic agent, and the carbon fiber paper iscarbonized to form the base layer.

However, when the base layer is manufactured by a roll to roll processaccording to a conventional method, there has been a problem that thebase layer is easily fractured by a small impact or depending on rolldriving conditions. The fracture of the base layer causes a problem thatthe production process yield and product quality deteriorate.

In particular, when a gas diffusion layer is formed as a thin filmaccording to the demand for making a fuel cell in a small size, thefracture problem of the base layer has occurred more easily. For thisreason, it has been difficult to secure mass productivity inmanufacturing the gas diffusion layer to have a thickness of 150 μm orless.

The contents described as the related art have been provided only toassist in understanding the background of the present disclosure andshould not be considered as corresponding to the related art known tothose having ordinary skill in the art.

SUMMARY

The present disclosure relates to a gas diffusion layer for a fuel cell,a method of manufacturing the same, and a unit cell for a fuel cellincluding the same. Particular embodiments relate to a gas diffusionlayer for a fuel cell having a continuous reinforcing portion, a methodof manufacturing the same, and a unit cell for a fuel cell including thesame.

An embodiment of the present disclosure provides a gas diffusion layerfor a fuel cell having a continuous reinforcing portion, a method ofmanufacturing the same, and a unit cell for a fuel cell including thesame.

According to an embodiment of the present disclosure, a gas diffusionlayer for a fuel cell constituting a unit cell of the fuel cell includesa base layer including short carbon fibers and having a reinforcingportion formed in a predetermined area thereof in a thickness directionwith continuous carbon fibers oriented in the reinforcing portion.

The continuous carbon fibers of the reinforcing portion formed in thebase layer may be oriented in one direction along a plane perpendicularto the thickness direction, while being spaced apart from each other.

Each of the continuous carbon fibers of the reinforcing portion may havea diameter of 6 to 12 μm.

The continuous carbon fibers of the reinforcing portion may be formed inbundles, each including a plurality of continuous carbon fibers, andeach of the bundles of continuous carbon fibers may have a thickness of50% or less of a total thickness of the base layer.

Each of the bundles of continuous carbon fibers in the reinforcingportion may be spaced apart from an adjacent bundle of continuous carbonfibers at a distance of 2 to 20 mm.

The reinforcing portion may be formed adjacent to a surface of the baselayer.

The gas diffusion layer may further include a micro porous layer formedon one surface of the base layer, and the reinforcing portion may beformed adjacent to a surface opposite to the surface on which the microporous layer is formed.

The gas diffusion layer may further include a micro porous layer formedon one surface of the base layer, and the reinforcing portion may beformed adjacent to the surface on which the micro porous layer isformed.

According to another embodiment of the present disclosure, a method ofmanufacturing a gas diffusion layer for a fuel cell constituting a unitcell of the fuel cell includes preparing a mixed dispersion in whichshort carbon fibers are mixed, orienting continuous carbon fibers on aconveyor belt, forming a paper having a reinforcing portion in which thecontinuous carbon fibers are oriented by supplying the prepared mixeddispersion to the conveyor belt on which the continuous carbon fibersare oriented, and forming a base layer by impregnating the paper with ahydrophobic agent.

In the orienting of the continuous carbon fibers, the continuous carbonfibers may be oriented in one direction, while being spaced apart fromeach other.

In the orienting of the continuous carbon fibers, the continuous carbonfibers may be prepared in bundles, each including a plurality ofcontinuous carbon fibers, and the bundles of continuous carbon fibersmay be oriented in close contact with or adjacent to a surface of theconveyor belt. In the forming of the paper, the mixed dispersion may besupplied to the surface of the conveyor belt at a thickness greater thanthat of each of the bundles of continuous carbon fibers.

In the forming of the paper, the mixed dispersion may be supplied at athickness at least two times greater than that of each of the bundles ofcontinuous carbon fibers.

In the orienting of the continuous carbon fibers, each of the continuouscarbon fibers forming the bundles may have a diameter of 6 to 12 μm, andeach of the bundles of continuous carbon fibers may be spaced apart froman adjacent bundle of continuous carbon fibers at a distance of 2 to 20mm.

The method may further include, after the forming of the base layer,forming a micro porous layer by applying a slurry in which a hydrophobicagent is mixed with carbon-based powder onto one surface of the baselayer. In the forming of the micro porous layer, the slurry may beapplied onto a surface opposite to a surface of the base layer on whichthe reinforcing portion is formed.

The method may further include, after the forming of the base layer,forming a micro porous layer by applying a slurry in which a hydrophobicagent is mixed with carbon-based powder onto one surface of the baselayer. In the forming of the micro porous layer, the slurry may beapplied onto a surface of the base layer on which the reinforcingportion is formed.

According to another embodiment of the present disclosure, a unit cellfor a fuel cell includes a membrane-electrode assembly (MEA), a pair ofgas diffusion layers (GDLs) disposed on both surfaces of themembrane-electrode assembly, respectively, and a pair of flow field typeseparators disposed on respective outer sides of the gas diffusionlayers and bent so that lands and channels are alternately formed,wherein each of the gas diffusion layers includes a base layer includingshort carbon fibers and having a reinforcing portion formed in apredetermined area thereof in a thickness direction with continuouscarbon fibers oriented in the reinforcing portion.

The continuous carbon fibers of the reinforcing portion formed in thebase layer of the gas diffusion layer may be oriented in one direction,while being spaced apart from each other.

The lands and the channels formed in the separator may be formed to bealigned in one direction, and a direction in which the continuous carbonfibers of the reinforcing portion are oriented may be kept at an angleof 45 to 90° with respect to a direction in which the lands and channelsof the separator are formed.

The base layer of the gas diffusion layer may be disposed to face theseparator, the gas diffusion layer may further include a micro porouslayer formed on one of both surfaces of the base layer facing themembrane-electrode assembly (MEA), and the reinforcing portion of thegas diffusion layer may be formed adjacent to the other one of bothsurfaces of the base layer facing the separator.

The base layer of the gas diffusion layer may be disposed to face theseparator, the gas diffusion layer may further include a micro porouslayer formed on one of both surfaces of the base layer facing themembrane-electrode assembly (MEA), and the reinforcing portion of thegas diffusion layer is formed adjacent to the one of both surfaces ofthe base layer facing the micro porous layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a typical unit cell for a fuel cell.

FIGS. 2 and 3 are views showing a gas diffusion layer for a fuel cellaccording to an embodiment of the present disclosure.

FIG. 4 is a view showing a gas diffusion layer for a fuel cell accordingto another embodiment of the present disclosure.

FIG. 5 is a view for explaining a process of manufacturing the gasdiffusion layer for a fuel cell according to an embodiment of thepresent disclosure.

FIGS. 6A to 8B are views for comparing the unit cell for a fuel cellaccording to an embodiment of the present disclosure with the typicalunit cell for a fuel cell.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described inmore detail with reference to the accompanying drawings. However, thepresent disclosure is not limited to the embodiments to be describedbelow and may be implemented in variously different forms. Theembodiments are provided to complete the present disclosure and forthose skilled in the art to completely understand the scope of thepresent disclosure. In the drawings, like reference numerals denote likecomponents.

FIGS. 2 and 3 are views showing a gas diffusion layer for a fuel cellaccording to an embodiment of the present disclosure.

As illustrated in FIGS. 2 and 3, a gas diffusion layer 100 for a fuelcell according to an embodiment of the present disclosure includes abase layer 120 including short carbon fibers 121 and having areinforcing portion no formed in a predetermined area thereof in athickness direction (x-axis direction) with continuous carbon fibers 111oriented in the reinforcing portion 110, and a micro porous layer 130formed on one surface of the base layer 120.

In this case, the micro porous layer 130 is formed to be identical orsimilar to a general micro porous layer applied to a typical gasdiffusion layer. For example, the micro porous layer 130 is formed byapplying a slurry, in which a hydrophobic agent such aspolytetrafluoroethylene (PTFE) is mixed with carbon-based powder such ascarbon black, onto one surface of the base layer 120. Then, the microporous layer 130 is formed in such a manner that some of the slurryapplied remains on one surface of the base layer 120 and the other ofthe slurry applied permeates into the surface of the base layer 120 by apredetermined depth. The micro porous layer 130 is not limited to theabove-described embodiment, and may be modified in various manners aslong as micro pores are formed to allow reaction gas to flow while beingdiffused therethrough.

Meanwhile, the base layer 120 is similar to a general base layermanufactured by impregnating a base in the form of carbon fiber paper orthe like made of short carbon fibers 121 with a hydrophobic agent suchas PTFE for imparting hydrophobicity, but the reinforcing portion no isformed in the predetermined area of the base layer 120 in the thicknessdirection (x-axis direction) with the continuous carbon fibers 111oriented therein.

The continuous carbon fibers 111 constituting the reinforcing portion110 formed in the base layer 120 are preferably oriented in onedirection, while being spaced apart from each other, so that tensileproperties of the continuous fibers are exhibited.

In this case, it is preferable that the direction in which thecontinuous carbon fibers 111 are oriented is variously modifieddepending on structures of the lands 31 and the channels 32 formed inthe separator 30. For example, the direction in which the continuouscarbon fibers 111 are oriented in the reinforcing portion 110 ispreferably kept at an angle of 45 to 90° with respect to a direction(y-axis direction) in which the lands 31 and the channels 32 of theseparator 30 are formed. Thus, the continuous carbon fibers 111 may beoriented in the reinforcing portion no in various directions, on a plane(y-z plane) perpendicular to the thickness direction (x-axis direction),depending on the structures of the lands 31 and the channels 32 of theseparator 30.

In addition, each of the continuous carbon fibers 111 forming thereinforcing portion 110 preferably has a diameter of 6 to 12 μm. It ispreferable to maintain the diameter of the continuous carbon fiber inwithin the proposed range for smooth diffusion and flow of reaction gasand generated water passing through the base layer 120. In particular,it is more preferable that the continuous carbon fiber in has a smallerdiameter within the proposed range. However, if the diameter of thecontinuous carbon fiber 111 is smaller than 6 μm, a desired level oftensile properties is not achieved.

In addition, the continuous carbon fibers 111 in the reinforcing portion110 are most preferably used as single strands, but may be formed andused in bundles, each including a plurality of continuous carbon fibers111, to express the tensile properties of the continuous carbon fibers111 at a desired level. In this case, each of the bundles of continuouscarbon fibers 111 preferably has a thickness d2 of 50% or less of atotal thickness of the base layer 120.

In addition, each of the bundles of continuous carbon fibers 111 in thereinforcing portion no is preferably kept spaced apart from an adjacentbundle of continuous carbon fibers 111 at a distance d1 of 2 to 20 mm.If the distance d1 between the bundles of continuous carbon fibers 111,which are spaced apart from each other, is smaller than 2 mm, thecontinuous carbon fibers 111 are of high density, resulting in anincrease in flow resistance of the reaction gas and generated water. Ifthe distance d1 between the bundles of continuous carbon fibers 111,which are spaced apart from each other, is greater than 20 mm, amechanical stiffness increasing effect of the reinforcing portion no isinsignificant.

Meanwhile, as illustrated in FIG. 3, the reinforcing portion 110 ispreferably formed adjacent to a surface of the base layer 120.

In this case, the reinforcing portion 110 is preferably formed adjacentto one of both surfaces of the base layer 120 opposite to the other oneof both surfaces of the base layer 120 on which the micro porous layer130 is formed. When forming a fuel cell stack, since the reinforcingportion 110 of the base layer 120 faces the separator 30, the base layer120 reinforced by the reinforcing portion no may be suppressed fromintrusion into the channels of the separator 30.

On the other hand, the location at which the reinforcing portion isformed in the base layer may be changed.

FIG. 4 is a view showing a gas diffusion layer for a fuel cell accordingto another embodiment of the present disclosure.

As illustrated in FIG. 4, like the gas diffusion layer in theabove-described embodiment, a gas diffusion layer 200 includes a baselayer 220 including short carbon fibers 221 and having a reinforcingportion 210 formed in a predetermined area thereof in a thicknessdirection (x-axis direction) with continuous carbon fibers 211 in thereinforcing portion 210, and a micro porous layer 230 formed on onesurface of the base layer 220.

However, concerning the reinforcing portion 210 formed adjacent to asurface of the base layer 220, in this case, the reinforcing portion 210is formed adjacent to one of both surfaces of the base layer 220 onwhich the micro porous layer 230 is formed. Accordingly, when the gasdiffusion layer 200 is manufactured, the micro porous layer 230 can beformed relatively uniformly, and it is possible to reduce damage to amembrane-electrode assembly (MEA) caused by ends of the short carbonfibers 221 forming the base layer 220. In addition, a pore gradient isformed sequentially in a direction from the micro porous layer 230through the reinforcing portion 210 and the base layer 220 to theseparator 30, thereby smoothly discharging the generated water andsupplying the reaction gas.

Next, a unit cell to which the gas diffusion layer according toembodiments of the present disclosure is applied will be described.

Like a typical unit cell for a fuel cell, the unit cell for a fuel cellto which the gas diffusion layer 100 having the reinforcing portion noformed therein is applied includes a membrane-electrode assembly 10; apair of gas diffusion layers 100 disposed on both surfaces of themembrane-electrode assembly 10, respectively; and a pair of flow fieldtype separators 30 disposed on respective outer sides of the gasdiffusion layers 100 and bent so that lands 31 and channels 32 arealternately formed.

In this case, as proposed in the above-described embodiment, the gasdiffusion layer 100 includes a base layer 120 including short carbonfibers 121 and having a reinforcing portion 110 formed in apredetermined area thereof in a thickness direction (x-axis direction)with continuous carbon fibers 111 oriented in the reinforcing portionno, and a micro porous layer 130 formed by impregnating a surface of thebase layer 120 with a slurry in which a hydrophobic agent is mixed withcarbon-based powder.

As the separator 30, a flow field type separator is applied. Forexample, the separator 30 is bent so that the lands 31 and the channels32 are alternately formed, the lands 31 are supported by the gasdiffusion layer 100, and reaction gas flows through the channels 32. Inthis case, the lands 31 and the channels 32 are formed to be aligned inone direction along a reaction gas flow direction.

In this case, a direction in which the continuous carbon fibers 111 ofthe reinforcing portion 110 are oriented is preferably kept at an angleof 45 to 90° with respect to a direction (y-axis direction) in which thelands 31 and the channels 32 of the separator 30 are formed. Whenforming a fuel cell stack, since the continuous carbon fibers 111 of thereinforcing portion 110 are disposed to cross the channels 32 of theseparator 30, the base layer 120 may be suppressed from intrusion intothe channels 32 of the separator 30.

If the angle between the direction in which the continuous carbon fibers111 of the reinforcing portion no are oriented and the direction inwhich the lands 31 and the channels 32 of the separator 30 are formed issmaller than 45°, the channels 32 of the separator 30 may be disposed tobe aligned with the direction in which the continuous carbon fibers 111are oriented, thereby causing a problem that the continuous carbonfibers 111 intrude into the channels 32 of the separator 30.

In addition, it is preferable that the base layer 120 of the gasdiffusion layer 100 is disposed to face the separator 30, and thereinforcing portion no of the gas diffusion layer 100 is formed adjacentto one of both surfaces of the base layer 120 facing the separator 30.Since the base layer 120 is reinforced by the reinforcing portion 110,the base layer 120 can be suppressed from intrusion into the channels 32of the separator 30.

Also, as in the above-described gas diffusion layer 200 according toanother embodiment, the base layer 220 of the gas diffusion layer 200may be disposed to face the separator 30, and the reinforcing portion210 of the gas diffusion layer 200 may be formed adjacent to one of bothsurfaces of the base layer 120 facing the micro porous layer 230.Accordingly, a pore gradient may be formed sequentially in the directionfrom the micro porous layer 230 through the reinforcing portion 210 andthe base layer 220 to the separator 30.

Next, a method of manufacturing the above-described gas diffusion layerwill be described.

FIG. 5 is a view for explaining a process of manufacturing the gasdiffusion layer for a fuel cell according to an embodiment of thepresent disclosure.

A method of manufacturing a gas diffusion layer according to anembodiment of the present disclosure includes preparing a mixeddispersion 121 a in which short carbon fibers 121 are mixed, orientingcontinuous carbon fibers 111 on a conveyor belt 1, forming a paperhaving a reinforcing portion 110 in which the continuous carbon fibers111 are oriented by supplying the prepared mixed dispersion 121 a to theconveyor belt 1 on which the continuous carbon fibers 111 are oriented,forming a base layer 120 by impregnating the paper with a hydrophobicagent, and forming a micro porous layer 130 by applying a slurry inwhich a hydrophobic agent is mixed with carbon-based powder onto asurface of the base layer 120.

The preparing of the mixed dispersion is preparing a mixed dispersion121 a in which short carbon fibers 121 are dispersed to form a baselayer 120. The mixed dispersion 121 a is prepared by mixing short carbonfibers 121, a binder, and a dispersant in a solvent.

In this case, water may be used as the solvent, and PAN-based shortcarbon fibers each having a length of 6 mm or 12 mm are used as theshort carbon fibers 121. Further, a PVA-based binder is used as thebinder.

The mixed dispersion 121 a prepared in this way is filled into a hopper3 provided above the conveyor belt 1.

The orienting of the continuous carbon fibers 111 is orientingcontinuous carbon fibers 111 in one direction to manufacture areinforcing portion 110 to be formed in the base layer 120. In thiscase, continuous carbon fibers 111 are unwound from a winding roll 2around which the continuous carbon fibers 111 are wound, and the unwoundcontinuous carbon fibers 111 are oriented in one direction in closecontact with or adjacent to a surface of the conveyor belt 1 while beingspaced apart from each other.

Here, the continuous carbon fibers 111 are most preferably oriented assingle strands, but may be formed in bundles, each including a pluralityof continuous carbon fibers in, and supplied to the conveyor belt 1.

In this case, each of the continuous carbon fibers 111 forming thebundles has a diameter of 6 to 12 μm, and the continuous carbon fibers111 are oriented so that each of the bundles of continuous carbon fibers111 is spaced apart from an adjacent bundle of continuous carbon fibers111 at a distance of 2 to 20 mm.

In forming of the paper, the mixed dispersion 121 a is supplied from thehopper 3 provided above the conveyor belt 1 to the surface of theconveyor belt 1 on which the continuous carbon fibers 111 are oriented.In this case, the mixed dispersion 121 a is preferably supplied at athickness greater than that of each of the bundles of continuous carbonfibers 111. More preferably, the mixed dispersion 121 a is supplied at athickness at least two times greater than that of each of the bundles ofcontinuous carbon fibers 111.

After supplying the mixed dispersion 121 a, in which the short carbonfibers 121 are mixed, to the continuous carbon fibers 111 as describedabove, the mixed dispersion 121 a is dried so that the short carbonfibers 121 and the continuous carbon fibers 111 are bound to each other,while the short carbon fibers 121 mixed in the mixed dispersion 121 aare primarily bound together, thereby forming the paper. The formedpaper may be cut to a desired size.

The forming of the base layer 120 is forming a base layer 120 in whichthe reinforcing portion no is formed. In forming of the base layer 120,first of all, the paper, that is, a carbon fiber web, is impregnatedwith a resin in which an inorganic filler is mixed, such that the shortcarbon fibers 121 mixed therein are secondarily bound together.Thereafter, the paper is carbonized through heat treatment at atemperature of about 1200 to 1400° C. Subsequently, in order to increasecarbon crystallinity of carbon components constituting the paper, thecarbon components are graphitized by additionally heat-treating thepaper at a temperature of 2000 to 2400° C.

The paper graphitized in this way is impregnated with a hydrophobicagent such as PTFE.

Thereafter, heat treatment is performed at a temperature correspondingto a melting point or higher of PTFE, e.g. about 350° C., to activatePTFE, thereby forming a base layer with water repellency imparted to thepaper.

The forming of the micro porous layer 130 is forming a micro porouslayer 130 by applying a slurry in which a hydrophobic agent is mixedwith carbon-based powder onto a surface of the base layer 120. First,the slurry is prepared by mixing carbon-based powder such as carbonblack and a hydrophobic agent such as PTFE in a solvent. The preparedslurry is applied onto the surface of the base layer 120, and then theslurry is dried to form a micro porous layer 130 on the surface of thebase layer 120.

Thereafter, heat treatment is performed at a temperature correspondingto a melting point or higher of PTFE, e.g. about 350° C., to activatePTFE, thereby imparting water repellency to the base layer 120 and themicro porous layer 130.

Meanwhile, in the forming of the micro porous layer 130, the slurry maybe applied onto a surface opposite to the surface of the base layer 120on which the reinforcing portion 110 is formed, or applied onto thesurface of the base layer 120 on which the reinforcing portion no isformed.

Next, the unit cell for a fuel cell in which the reinforcement portionis formed in the base layer according to an embodiment of the presentdisclosure will be compared with the typical unit cell for a fuel cellin which no reinforcement portion is formed in the base layer.

FIGS. 6A to 8B are views for comparing the unit cell for a fuel cellaccording to an embodiment of the present disclosure with the typicalunit cell for a fuel cell. In this case, FIGS. 6A, 7A, and 8A are viewsshowing the typical unit cell for a fuel cell in which no reinforcementportion is formed in the base layer, and FIGS. 6B, 7B, and 8B are viewsshowing the unit cell for a fuel cell in which the reinforcement portionis formed in the base layer according to an embodiment of the presentdisclosure. In addition, FIGS. 7A and 7B show cross-sections cut alongline A-A′ of FIGS. 6A and 6B, respectively, and FIGS. 8A and 8B showcross-sections cut along line B-B′ of FIGS. 6A and 6B, respectively.

As illustrated in FIG. 6B, the membrane-electrode assembly 10, the gasdiffusion layer 100, and the separator 30 are sequentially stacked inthe unit cell for a fuel cell. In this case, the base layer 120 formingthe gas diffusion layer 100 faces the separator 30, and the micro porouslayer 130 faces the membrane-electrode assembly 10. In addition, as theseparator 30, a flow field type separator in which lands 31 and channels32 are formed is applied.

In particular, in the gas diffusion layer 100 of the unit cell for afuel cell according to an embodiment of the present disclosure, asillustrated in FIG. 6B, the reinforcing portion 110 including thecontinuous carbon fibers 111 oriented in one direction is disposedadjacent to a surface of the base layer 120 facing the separator 30.

In the unit cell for a fuel cell according to an embodiment of thepresent disclosure, the gas diffusion layer 100 and the separator 30 arestacked so that the direction in which the continuous carbon fibers 111are oriented is kept at an angle of 90°, that is orthogonal, withrespect to the direction (y-axis direction) in which the channels 32 ofthe separator 30 are formed.

As illustrated in FIG. 7A, in the typical unit cell for a fuel cell,while the gas diffusion layer 20 is stacked to face the separator 30,the base layer 21 partially intrudes into the channels of the separator30 (I), resulting in a deformation of the gas diffusion layer 20. Thedeformation of the gas diffusion layer 20 causes a differential pressurebetween the channels 32, resulting in a problem that the performance ofthe fuel cell stack deteriorates.

On the other hand, as illustrated in FIG. 7B, in the unit cell for afuel cell according to an embodiment of the present disclosure, whilethe gas diffusion layer 100 is stacked to face the separator 30, thereinforcing portion no formed in the base layer 120 of the gas diffusionlayer 100 suppresses the base layer 120 from partially intruding intothe channels 32 of the separator 30, thereby preventing a differentialpressure between the channels 32.

In addition, as illustrated in FIG. 8A, in the typical unit cell for afuel cell, when the base layer 21 of the gas diffusion layer 20 and thechannels 32 of the separator 30 are in contact with each other, aseparate water discharge passage for the generated water is not formed.In contrast, as illustrated in FIG. 8B, in the unit cell for a fuel cellaccording to an embodiment of the present disclosure, a passage fordischarging the generated water W is formed in a space between thecontinuous carbon fibers 111 forming the reinforcing portion 110, whichare spaced apart from each other. Thus, it is possible to expect aninducing effect for the generated water W to be smoothly discharged.

According to the embodiments of the present disclosure, the followingeffects can be expected.

First, due to the tensile properties of the continuous carbon fibersapplied to the reinforcing portion, it is easy to produce a base in aroll type with excellent handling properties, thereby increasing aproduction yield in the gas diffusion layer manufacturing process andlowering a failure rate in the stack formation process. As a result,productivity can be increased and cost can be reduced.

Second, the reinforcing portion formed in the base layer increases ashear strength of the gas diffusion layer. Thus, even if the base layerfor the gas diffusion layer is manufactured to have a thickness of 100μm or less, no fracture occurs. Accordingly, mass productivity can besecured in manufacturing gas diffusion layers as thin-film in a roll toroll type.

Third, by stacking the gas diffusion layer and the separator so that theangle between the direction in which the continuous carbon fibers of thereinforcing portion formed in the base layer are oriented and thedirection in which the lands and the channels of the flow field typeseparator are formed is kept within the range of 45 to 90°, when forminga fuel cell stack, the gas diffusion layer can be suppressed fromintrusion into the channels of the separator, thereby reducing adifferential pressure between the channels. As a result, the performanceof the fuel cell stack can be improved.

Fourth, by stacking the gas diffusion layer and the separator so thatthe angle between the direction in which the continuous carbon fibers ofthe reinforcing portion formed in the base layer are oriented and thedirection in which the lands and the channels of the flow field typeseparator are formed is kept within the range of 45 to 90°, a surfacepressure against reaction formed in the channels of the separator can beincreased, thereby reducing a contact resistance. As a result, theperformance of the fuel cell stack can be improved.

Although the present disclosure has been shown and described withrespect to specific embodiments, it will be apparent to those havingordinary skill in the art that the present disclosure may be variouslymodified and altered without departing from the spirit and scope of thepresent disclosure as defined by the following claims.

What is claimed is:
 1. A gas diffusion layer for a fuel cellconstituting a unit cell of the fuel cell, the gas diffusion layercomprising: a base layer including short carbon fibers and having areinforcing portion formed in a predetermined area thereof in athickness direction with continuous carbon fibers oriented in thereinforcing portion.
 2. The gas diffusion layer of claim 1, wherein thecontinuous carbon fibers of the reinforcing portion formed in the baselayer are oriented in one direction along a plane perpendicular to thethickness direction, while being spaced apart from each other.
 3. Thegas diffusion layer of claim 1, wherein each of the continuous carbonfibers of the reinforcing portion has a diameter of 6 to 12 μm.
 4. Thegas diffusion layer of claim 3, wherein: the continuous carbon fibers ofthe reinforcing portion are formed in bundles, each of the bundlesincluding a plurality of the continuous carbon fibers; and each of thebundles of the continuous carbon fibers has a thickness of 50% or lessof a total thickness of the base layer.
 5. The gas diffusion layer ofclaim 4, wherein each of the bundles of the continuous carbon fibers inthe reinforcing portion is spaced apart from an adjacent bundle of thecontinuous carbon fibers at a distance of 2 to 20 mm.
 6. The gasdiffusion layer of claim 1, wherein the reinforcing portion is formedadjacent to a first surface of the base layer.
 7. The gas diffusionlayer of claim 6, further comprising a micro porous layer formed on asecond surface of the base layer, wherein the first surface of the baselayer is opposite the second surface of the base layer.
 8. The gasdiffusion layer of claim 6, further comprising a micro porous layerformed on the first surface of the base layer.
 9. A method ofmanufacturing a gas diffusion layer for a fuel cell constituting a unitcell of the fuel cell, the method comprising: preparing a mixeddispersion in which short carbon fibers are mixed; orienting continuouscarbon fibers on a conveyor belt; forming a paper having a reinforcingportion in which the continuous carbon fibers are oriented by supplyingthe prepared mixed dispersion to the conveyor belt on which thecontinuous carbon fibers are oriented; and forming a base layer byimpregnating the paper with a hydrophobic agent.
 10. The method of claim9, wherein in the orienting of the continuous carbon fibers, thecontinuous carbon fibers are oriented in one direction, while beingspaced apart from each other.
 11. The method of claim 9, wherein: in theorienting of the continuous carbon fibers, the continuous carbon fibersare prepared in bundles, each of the bundles including a plurality ofthe continuous carbon fibers, and the bundles of the continuous carbonfibers are oriented in close contact with or adjacent to a surface ofthe conveyor belt; and in the forming of the paper, the mixed dispersionis supplied to the surface of the conveyor belt at a thickness greaterthan that of each of the bundles of the continuous carbon fibers. 12.The method of claim 11, wherein in the forming of the paper, the mixeddispersion is supplied at a thickness at least two times greater thanthat of each of the bundles of the continuous carbon fibers.
 13. Themethod of claim 11, wherein: in the orienting of the continuous carbonfibers, each of the continuous carbon fibers forming the bundles has adiameter of 6 to 12 μm; and each of the bundles of the continuous carbonfibers is spaced apart from an adjacent bundle of the continuous carbonfibers at a distance of 2 to 20 mm.
 14. The method of claim 11, furthercomprising, after the forming of the base layer, forming a micro porouslayer by applying a slurry in which a hydrophobic agent is mixed withcarbon-based powder onto a first surface of the base layer, wherein thefirst surface is opposite a second surface of the base layer on whichthe reinforcing portion is formed.
 15. The method of claim 11, furthercomprising, after the forming of the base layer, forming a micro porouslayer by applying a slurry in which a hydrophobic agent is mixed withcarbon-based powder onto a surface of the base layer on which thereinforcing portion is formed.
 16. A unit cell for a fuel cell, the unitcell comprising: a membrane-electrode assembly; a pair of gas diffusionlayers disposed on outer surfaces of the membrane-electrode assembly,respectively, wherein each of the gas diffusion layers includes a baselayer including short carbon fibers and having a reinforcing portionformed in a predetermined area thereof in a thickness direction withcontinuous carbon fibers oriented in the reinforcing portion; and a pairof flow field type separators disposed on outer sides of the gasdiffusion layers, respectively, and bent so that lands and channels arealternately formed.
 17. The unit cell of claim 16, wherein thecontinuous carbon fibers of the reinforcing portion formed in the baselayers of the gas diffusion layers are oriented in one direction, whilebeing spaced apart from each other.
 18. The unit cell of claim 17,wherein: the lands and the channels formed in the separators are formedto be aligned in one direction; and a direction in which the continuouscarbon fibers of the reinforcing portion are oriented is kept at anangle of 45 to 90° with respect to the direction in which the lands andthe channels of the separators are formed.
 19. The unit cell of claim16, wherein: the base layers of the gas diffusion layers are disposed toface the separators; the gas diffusion layers further include a microporous layer formed on a first surface of the base layers facing themembrane-electrode assembly; and the reinforcing portions of the gasdiffusion layers are formed adjacent to a second surface of the baselayers facing the separators.
 20. The unit cell of claim 16, wherein:the base layers of the gas diffusion layers are disposed to face theseparators; the gas diffusion layers further include a micro porouslayer formed on a first surface of the base layers facing themembrane-electrode assembly; and the reinforcing portions of the gasdiffusion layers are formed adjacent to the first surface of the baselayer facing the micro porous layer.